Process of making insulated electrical conductors



INVENTQR it, fiifleesaio A H15 ATTORNEY N 1 5 \\N\ N N\\\\\\NN\\ \\\\\\\\\\N \\\\\\\\\\\\\\\\\\\\\\\\\\N I N m M EU N ngbmw Raga? Filed Jan. 24, 1946 W EwmwMMA/AJ H Feb. 21, 1950 E w BREISCH PROCESS OF mmc msuumn ELECTRICAL CONDUCTORS Patented Feb. 21, 1950 UNITED STATES PATENT OFFICE PROCESS OF MAKING INSULATED ELECTRICAL OONDUCTORS Edgar W. Breisch. Edgewood, Pa assignor to The Union Switch & Signal Company, Swissvale, Pa a corporation of Pennsylvania Application January 24, 1948, Serial No. 643,102-

1 Claim. (01'. z9 14s.z)

My invention relates to the process of making an insulated electrical conductor.

An insulated electrical conductor of relatively rugged construction is frequently required. For example, in railway train communication equipment which employs a loop circuit on the vehicle of a train and which loop circuit includes a conductor mounted lengthwise of the vehicle and vertical at each end of the vehicle, a conductor of rugged construction is required. Such a conductor is in a position to be taken hold of by the train crew and also to be gripped as a hand rail. The position of such conductors makes them subject to severe abuse and almost constant vibration. Thus, such a conductor must be of a rugged construction to give it the necessary strength and it must be well insulated to protect the train crew from shock and to protect the communication equipment from circuit faults. Also, the insulation needs to be held firmly in place because when the conductor is used as a hand rail loosely applied insulation'might startle a man and cause him to relinquish his grip. Furthermore, in train communication equipment of the type here involved, the conductor of the loop circuit should have a relatively high conductivity for current of relatively high frequency.

Accordingly, an object of my invention is the provision of an improved process for manufacturing electrical conductors of the type here contemplated.

Other features, objects and advantages of 'my invention will appear as the specification progresses.

I attain the foregoing features, objects and ad vantages of my invention by constructing a conductor out of tubing of diiierent materials and which tubes are shrunken into place one over the other, to form a firm mechanical structure, having high mechanical strength, high conductivity and high insulation resistance. An inner tube is made of a material, such as steel, to give the conductor high strength, a second tube shrunken over the first tube is of a material, such as copper, to give the conductor relatively high conductivity, and an outer tube of elastic insulating material, such as extruded rubber, is shrunken over the second tube to give the conductor a relatively high insulation resistance.

To provide such a conductor, I use tubes, the inside diameter of which is not greater than the an insulated electrical conductor according my. invention, and shall then point out the novelf features of the manufacturing process-in a In the accompanying drawings. Flcrlis' a grammatic sectional view showing one form jof an electrical conductor embodying my invention, and r a Fig. 2 is a diagrammatic view showing a preferred process of manufacturing the conductor of Fig. 1, and which process also embodies my invention.

In each of the two views like reference characters are used to designate similar parts.

Referring to Fig. 1, the reference character CN designates a conductor embodying my invention and of which conductor a tube I serves as an inner tube, the tube I being of a material of high strength such as steel. The tube I is of a size and thickness preselected as may be required for the particular conductor. For example, in a loop circuit conductor for train communication systems, the tube I may be a steel tube having an inside diameter of one inch and an outside diameter of 1%, inches. It is to be understood that the invention is not limited to such a steel tube and a tube of other material and dimensions can be used.

A tube 2 is disposed outside of the tube I. 'lhis tube 2 is of a material of relatively high conductivity such as copper. The copper tube 2 is shrunken over the steel tube I to insure firm intimate contact between the two tubes. Preferably the copper tube 2 has an inside diameter equal to or slightly less than the outside diameter of the steel tube I. In the case the inner tube I has an outside diameter of 1 inches as used hereinbefore for the purpose of illustration,the copper tube 2 may be one having an inside diameter of 1 inches and 11; inches outside diameter, making the tube a; of an inch thick. To shrink tube 2 over the tube I the tubes are brought to unequal temperatures to expand or contract one or the other of the tubes with respect to the other tube and then while one' tube is temporarily expanded or contracted the outside diameter of the tube over which the first tube is to be disposed. I also provide a novel process for expanding or contracting a tube temtwo tubes are slipped one over the other and the tubes allowed to return to their normal temperatures. The process of bringing the two tubes to an unequal temperature can be accomplished in several diflerent ways, and I prefer to heat the copper tube in a furnace while leaving the steel tube at room temperature and then slide the copper tube over the steel tube as the copper.

tube is drawn from the furnace. In this way the tubes can be of considerable length and the copper tube drawn into place-before any part of it cools. Again, the steel tube can be placed in a bath of a freezing mixture or packed in Dry Ice whfle the copper tube is left at room temperature and the steel tube slid into the copper tube as it is drawn from the 'bath. Also, the copper tube can be heated by passing the tube through a coil carrying a high frequency current and the tube heated by induction, and the tube slipped over the steel tube as it is drawn from the coil. the copper tube moving at a speed sufficient for it to be slipped into place before any portion of the copper tube cools.

An insulation tube 3 is then disposed over the combined copper and steel tube. This insulating tube 3 can be of any suitable insulating material having suflicient elasticity. For example, the tubing 3 can be of extruded rubber composition. To insure a firm grip between the tube 3 and the tube 2, the tube 3 is of an inside diameter equal to or less than the outside diameter of the copper tube. In the case assumed hereinbefore if the copper tube has an outside diameter of 11% inches, the tube 3 would have an inside diameter of say 1% inches.

In Fig. 2, there is illustrated a preferred process of placing the insulation tube 3 over the combined copper and steel tube. In Fig. 2, a stand 4 is secured to a working surface 5 as by lag screws 6. A pipe member I, having its outer surface threaded, has one end fixed in the stand 4 by being screwed into a. threaded bore of the stand. A hand wheel 8 is provided with a threaded borev which mates with the outer threaded surface of the free end of pipe member l and the hand wheel 8 can be moved back and forth longitudinally along the member 3 by the turning of the wheel.

A mandrel 9 fits inside the pipe member 1 and is held firmly in place therein through a threaded portion mating with inside threads of the pipe member J. The mandrel 9 is of some length to extend outside the member if to the right as viewed in Fig. 2. This extension of the mandrel Q'is stepped to form an enlarged portion ii at its free end, the diameter of the portion l i being just slightly less than the inside diameter of the steel tube I of the conductor. A sleeve l2 slidably fits on the smaller portion ill of the mandrel 9 and is provided with a collar l3 against which a hub of the handwheel 8 engages when the wheelis run out on the member l.

.The sleeve I2 is of a diameter substantially the same as the outside diameter of the copper tube 2 of the conductor and its end opposite the collar i3 is turned down so that it fits inside the steel tube I of the conductor. A felt ring i5 is disposed between the free end of the sleeve l2 and the shoulder of the enlarged portion ll of the mandrel.

It is clear that the combined steel and copper tube of the conductor can be slid over the enlarged portion of the mandrel, felt ring it and the turned down portion M of the sleeve 52, and

that the hand wheel 8 when run out on the mem- 4 felt ring I! being somewhat compressed to aid in forming an air tight joint.

A port it; is drilled the entire length of the mandrel 9 and the end of the mandrel adjacent the support 4 is drilled and threaded to receive a coupling ll of a hose I8. The hose i8 is connected to a suitable source of air pressure, not shown, such connection preferably including a standard form of valve and gauge to aid in control of air pressure to and from the port l6.

In placing the insulation tube 3 over the combined steel and copper tube, a required length of the combined steel and copper tube is prepared and one end thereof is anchored by being slid over the mandrel and sleeve and the hand wheel run out for sleeve ii to engage this end of the tube as explained above. Supporting rollers !9 are preferably mounted on the working surface 5 to hold the tube in alignment because the free end of the tube tends to sag when the tube is of considerable length.

A length of insulation tubing 3 is cut to be slightly longer than the length of the steel-copper tube. A flanged collar 20 is inserted in one end of the tube 3 and the tube firmly gripped by a clamp 2| to form an air tight joint between the tube 3 and the collar 20. The inside diameter of the collar 20 is just slightly greater than the outside diameter of the copper tube 2, so that the collar with tube 3 attached can be slid along the tube 2. A plug 22 is inserted in the other end of the insulation tube 3 and a clamp 23 placed over the tube to grip the tube to the plug to form a substantially air tight joint.

The collar 20 is then started on to the free end of the steel-copper tube and air pressure admitted through connection l8 and port is of the mandrel to the inside of the tubes. This pressure in tube 3 causes the tube 3 to expand and while in such expanded condition the collar 20 and tube 3 are pulled along the full'length of the steel-copper tube until collar 2%) slides onto the sleeve 92. It is to be noted that the steelcopper tube is flexible enough to permit the collar 2% to pass over the rollers l9. Also when the tube is thus in place the plug 22 will be a little back from the free end of the steel-copper tube. There will be some leaking of the air pressure around the collar 20 but such pressure serves to keep the insulation tube 8 expanded as it is being pulled over the steel-copper tube.

With the insulation tube 3 in place the air pressure is exhausted and the tube 3 contracts to grip the steel-copper tube with a firm mechanical contact. The clamps 2i and 23 are now removed and the insulation tube 3 trimmed to the length of the steel-copper tube, the tube 3 being preferably left a little long to protect the ends of the steel-copper tube during shipment. It is to be observed that the insulation tube need not be first cut to suit the conductor to be formed but instead the tube 3 may be compressed by a clamp to form an air tight joint to form a portion some greater in length than the conductor and the tube 3 out after in place. This may eliminate scraps of the insulation tube.

By such a process the conductor CN can be built up comparatively quickly and at a relatively low cost and the conductor is one having high strength, high conductivity and high insulation resistance. Also the assembly is of a rugged construction and will withstand abuse and vibration and it can be used as a hand rail.

Although I have hereinshown and described only one form of electrical conductor, and a preferred process of making the conductor, embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claim without departing from the spirit and scope of my invention.

Having thus described my invention, what I claimis:

The process of manufacturing an insulated electrical conductor which consists of preparing a given length of a first tube which has a preselected outside diameter and a relatively high conductivity, preparing a second tube of elastic insulating material of a length a little greater than said given length and having an inside diameter no greater than said outside diameter of said first tube, clamping one end of said second tube to form an air tight joint, clamping the other end of said second tube over a collar having an inside diameter slightly greater than said outside diameter of said first tube, mounting the first tube in a horizontal place and slipping one end of the tube over a mandrel to anchor the tube at the one end and leaving its other end free, starting said collar with said second tube attached over the free end of said first tube, admitting air pressure to the inside of the anchored end of the first tube for the pressure to flow through the first tube and into the second tube to expand said second tube, pulling the collar and second tube over the first tube while the first tube is supported in its horizontal position, and exhausting said air pressure for said second tube to contract and grip said first tube.

EDGAR W. BREISCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

